Wave Propagation Behavior Research Articles

Impact-Echo for Crack Detection in Concrete with Artificial Intelligence based on Supervised Deep Learning

Aging concrete infrastructure such as bridges and tunnels need to be appropriately maintained in their service life because these structures must be employed with ensured safety level. Inspection and maintenance with reasonable measures are typically operated for the reinforced concrete before severe damage and failure are developed. Especially, the crack propagation in concrete can significantly affect the structural integrity, durability and overall performance of structural elements. Effective maintenance strategies are required for material and structural assessment with detection and repair of cracks to prevent further deterioration. Identification of cracks in concrete is effectively operated to extend the service life of structures for mitigating the potential safety hazards and minimize the repair costs. In order to detect the cracks in the concrete structure member, non-destructive testing (NDT) system can be often introduced to satisfy the technical issues in terms of damage evaluation and estimation of repair condition. Currently, various NDT methods have been utilized for quantitative analysis of internal damage/defects using elastic wave method such as impact-echo method, focusing on reflection of P-wave in concrete as wave propagation behavior. In experimental laboratory tests, concrete specimens are usually prepared with interior damages (cracks) which are simulated as embedded plastic plate or styrofoam. In this study, starch- type polysaccharide sheet is used to form the simulated cracks in concrete specimen. This study aims at applying impact-echo method with AI (Artificial Intelligence) to identify the internal crack information based on the waveform characteristics obtained from the elastic wave propagation behavior. The waveform results are converted to frequency spectrum by FFT analysis. Consequently, it is found in this study that AI, which is employed by supervised deep learning models, successfully evaluates the data and displays the probability of crack existence in concrete. Since FFT is a powerful algorithm that quickly converts a signal from the time domain to the frequency domain, it gives efficient analysis to the impact echo method for crack detection with the application of AI system.

Band gap study of periodic piezoelectric micro-composite laminated plates by finite element method and its application in feedback control

Phononic crystals are materials or structures with periodic variations of elastic constants and density. Elastic waves in phononic crystals cannot propagate within a certain frequency range, called the band gap, due to the interference of their internal structure. This article investigates how fiber orientation affects the band gap properties of periodic micro-composite laminated plates. We examined the impact of five common composite laminate configurations on the system’s band gap and discovered that the antisymmetric configuration had superior high-frequency band gap performance. Based on this finding, we further explored how the antisymmetric angle influenced the system’s band gap. Since the study was conducted at a micro scale, micro structural effects were considered. Therefore, we used the modified coupled stress elastic dynamics and a four-node quadrilateral non-conforming element to discretize the micro composite laminated plate model, which had the nodal compatibility of high-order elasticity theory. Moreover, we employed feedback control to the proposed structure to dynamically adjust the band gap width according to different practical needs. This research supports the design of periodic micro-composite laminated plates and the piezoelectric feedback control system, which can control the vibration and wave propagation behaviors of micro structures using coupled piezoelectric sensors and actuators. The piezoelectric feedback control employed two control methods: direct proportional control and acceleration control. This article compared the single and multiple control methods of these two approaches to determine the optimal control strategy.

Nonlinear thermoelastic wave propagation in general FGM sandwich rectangular plates

The present work is dedicated to investigating the thermoelastic wave propagation behavior of sandwich rectangular plates (SRP) made of functionally graded material (FGM). The main contribution lies in the partial modification of basic theoretical expressions and solution methods to improve the accuracy of practical system models. An analytical model with three types of general configurations is established. The porosity distribution in FGM layers depends on the degree of mixture of the constituent materials, with the FGM layers without porosity taken as a reference model. The effect of porosity within FGMs is addressed through a refined analytical formulation of material properties, and the temperature-dependent material properties of FGM sandwich structures (FGMSS) maintain continuity through the thickness. This improved framework introduces a porosity function encompassing three distinct structural and geometrical functions: the core-to-thickness ratio (CTR), porosity volume fraction (PVF), and porosity distribution function (PDF). It is worth mentioning that the theoretical expressions maintain good continuity and reliability under the influence of thermal conditions and system parameters of the proposed structures. Furthermore, considering the generation of thermal strain energy (TSE) caused by thermal expansion of the structure in the normal direction, an improved analytical approach for determining TSE in rectangular plate structures is then investigated by introducing the Green's nonlinear strain (GNS). Hamilton's principle is applied to derive the wave motion equations and analytical solutions for the wave dispersion relations are derived. Furthermore, accurate numerical simulation is performed and the solution is verified with data available in published resources. In addition, we present a systematic parametric analysis to examine the effects of porosity, configuration, power-law exponent (PLE), PVF, CTR, temperature, and wave number on the thermoelastic wave propagation behavior of FGMSRP.

Negative refraction of elastic waves in two-dimensional inertial amplification metamaterials

Tailoring wave behaviors governed by dispersion relations is a huge challenge in wave manipulation. Inertial amplification (IA) mechanism has been introduced in metamaterials and phononic crystals to obtain a low-frequency bandgap without adding mass to the system. In this work, we demonstrate unique wave propagation behaviors in two-dimensional inertial amplification metamaterials (2D IAMs). Through analytical derivations and numerical simulations, negative refraction and refractive steering of elastic waves are realized with the IA mechanism. The positive (negative) inertia of the system can be tuned by the IA angle, which determines whether the passband of the lattice is positive (negative) group velocity. By analyzing the dispersion relations of the 2D IAMs, we find that the IA angle 45° is the critical point where the group velocity flips. Negative refraction occurs at the interface between two lattices, which have opposite signs of group velocity. We can also achieve a wide range of angles for wave steering in the system. The normalized displacement fields of 2D IAMs are measured via harmonic excitation. We believe that the research results may inspire the design of ‘elastic lenses’ and multifunctional metamaterial devices.

Study on dynamic characteristics of cavitation in underwater explosion with large charge

Underwater explosions (UNDEX) generate shock waves that interact with the air–water interface and structures, leading to the occurrence of rarefaction waves and inducing cavitation phenomena. In deep-water explosions, complex coupling relationships exist between shock wave propagation, bubble motion, and cavitation evolution. The shock wave initiates the formation of cavitation, and their growth and collapse are influenced by the pressure field. The collapsing bubbles generate additional shock waves and fluid motion, affecting subsequent shock wave propagation and bubble behavior. This intricate interaction significantly impacts the hydrodynamic characteristics of deep-water explosions, including pressure distribution, density, and phase changes in the surrounding fluid. In this paper, we utilize a two-fluid phase transition model to capture the evolution of cavitation in deep-water explosions. Our numerical results demonstrate that the introduction of a two-phase vapor–liquid phase change model is necessary to accurately capture scenarios involving prominent evaporation or condensation phenomena. Furthermore, we find that the cavitation produced by the same charge under different explosion depths exhibits significant differences, as does the peak value of cavitation collapse pressure. Similarly, the cavitation produced by different charge quantities under the same explosion depth varies, and the relationship between cavitation volume and charge quantity is not a simple linear increase. The research methods and results presented in this paper provide an important reference for studying the dynamic characteristics of deep-water explosions.

A novel approach for generalized Green-Naghdi-type electro-magneto-thermo-hyperelasticity wave propagation and reflection investigations in near-incompressible layers under shock loads

A novel nonlinear coupled finite-strain electro-magneto-thermo-hyperelasticity (EMTHE) model is developed for the first- and second-sound wave propagation and reflection investigations in media that are exposed to electromagnetic fields and mechanical shocks. In contrast to the previous studies which studied behaviors of the finite-strain elastic or incompressible materials with small deformations, the current research proposes a much more complicated but much more accurate novel practical model for wave propagation and reflection analyses in near-incompressible finite-strain materials. Furthermore, to evaluate the effects of the electro-magneto-thermomechanical coupling, the strain energy density function of the hyperelastic material is expanded in a new way. The governing equations are obtained according to a nonlinear version of the Helmholtz free energy. The energy equations comprise the first- and second-order time rates of the temperature to enable the modeling of the finite-speed heat transfer; i.e., the establishment of a second-sound model. A nonlinear iterative finite element solution algorithm is proposed and implemented for the resulting coupled time-dependent generalized electro-magneto-thermo-hyperelasticity equations. The results show significant differences between the predicted wave propagation and reflection characteristics and behaviors of the near-incompressible and incompressible finite-strain models.

Topological valley mode separation of elastic waves and potential applications

Topological metamaterials in condensed matter systems have shown significant potential for information and energy applications due to their novel wave propagation behaviors. Recently, there has been an increasing focus on studying topological metamaterials in classical wave systems. Elastic waves, as full-vector classical waves, possess more intricate mechanical characteristics compared to sound waves and electromagnetic waves. This complexity not only offers diverse practical application possibilities but also presents notable research challenges in the field of topological metamaterials. In this study, our main objective is to achieve the ideal mode separation of elastic waves, specifically separated into the in-plane and out-of-plane components, and explore its potential applications. Firstly, we design phononic crystals with dual Dirac cones. Through geometric perturbation, we successfully separate the valley Hall phases of in-plane and out-of-plane modes. By superimposing different topological phases, we achieve three types of topological edge states: in-plane waves, out-of-plane waves, and hybrid waves. Combining these different topological edge states enables us to effectively separate the elastic waves into in-plane and out-of-plane components. Furthermore, we investigate the potential application of mode separation in energy harvesting. We achieve the energy localization of different wave modes based on the topological whispering-gallery mode. Additionally, by utilizing piezoelectric materials, we realize the subregional energy harvesting of in-plane and out-of-plane modes. The mechanical properties resulting from mode separation and topological whispering-gallery mode hold great potential for signal filtering and energy storage, thereby opening up new possibilities for controlling and utilizing elastic waves in various engineering scenarios.

Analytical assessment of wave dynamics for natural fibre-reinforced composite plates

This study presents a mathematical modelling to investigate the wave propagation behaviour in laminated natural fibre-reinforced composite plates integrated with surface bonded piezoelectric materials. To model wave dynamics, the constitutive relations, and governing equations of wave motion are derived based on different plate theories and Maxwell's electricity equation due to the surface bonded piezoelectric materials with the closed-circuit electrical boundary condition and transverse poling direction. The influence of natural fibres, as the reinforcing material of the host laminated composite plate, on wave propagation is studied and compared with the effects of synthetic fibres (i.e., carbon, Kevlar, and E-glass). The effects of other factors such as fibre volume fraction, laminate stacking sequence, and the presence of piezoelectric materials on wave dynamics are also investigated. The results of the wave propagation analysis reveal that the impact of different parameters on wave dynamics depends on the range of wavenumbers and wave mode numbers considered. It is found that some parameters may exhibit a noticeable influence on wave velocities, while others may have a negligible effect. The effect of piezoelectric materials on wave velocities in composite plates reinforced with natural fibres e.g., bamboo fibres, may differ from that observed in synthetic fibre-reinforced composite plates.

Toward Deep Generation of Guided Wave Representations for Composite Materials

Laminated composite materials are widely used in most fields of engineering. Wave propagation analysis plays an essential role in understanding the short-duration transient response of composite structures. The forward physics-based models are utilized to map from elastic properties space to wave propagation behavior in a laminated composite material. Due to the high-frequency, multi-modal, and dispersive nature of the guided waves, the physics-based simulations are computationally demanding. It makes property prediction, generation, and material design problems more challenging. In this work, a forward physics-based simulator such as the stiffness matrix method is utilized to collect group velocities of guided waves for a set of composite materials. A variational autoencoder (VAE)-based deep generative model is proposed for the generation of new and realistic polar group velocity representations. It is observed that the deep generator is able to reconstruct unseen representations with very low mean square reconstruction error. Global Monte Carlo and directional equally-spaced samplers are used to sample the continuous, complete and organized low-dimensional latent space of VAE. The sampled point is fed into the trained decoder to generate new polar representations. The network has shown exceptional generation capabilities. It is also seen that the latent space forms a conceptual space where different directions and regions show inherent patterns related to the generated representations and their corresponding material properties.

A novel 3D topological metamaterial for controllability of polarization-dependent multilayer elastic waves

The achievement of high-quality wave manipulation and energy concentration has always been considered as state-of-the-art technologies, especially for integrated photonics, acoustics, and mechanics. The exploration of the topological phase of matter provides abundant design tools for robust waveguiding that is immune to backscattering at small defects and sharp bends. Recent research has extended the elastic wave manipulation from 2D edge waveguiding to 3D planar waveguiding. However, most of them are limited to single-mode and single-frequency wave propagation along the designed plane. This paper introduces a novel 3D topological metamaterial structure whose geometrical parameters are specifically configured to obtain dual-mode topological states at distinct frequencies. Parametric studies are presented to demonstrate the controllability of bandgaps and to provide a design principle for preventing the effects of unwanted modes. Topological interface modes with either high group velocity or near-zero group velocity along the z direction are found. Full-scale finite element simulations are presented to uncover the elastic wave propagation behavior. The interesting layer-locked and layer-unlocked waveguiding based on excitation polarization and frequency for both straight path and zig-zag path are demonstrated. The outcomes of this work suggest abundant potential applications related to elastic wave control such as wave filters, energy harvesters, mechanical computers, and the like. This work may also help inspire future research on more complex and sophisticated multi-mode waveguiding in 3D spaces.

Investigation on the propagation characteristics of pressure wave during managed pressure drilling

The small difference between formation pressure and fracture pressure in offshore oil and gas reservoirs poses a huge challenge to drilling. Managed pressure drilling (MPD) technology, as a drilling technique that can accurately control bottomhole pressure, is an effective technique to solve this challenge. In MPD technology, the pressure wave propagation behavior and mechanism in the wellbore induced by wellhead backpressure are crucial for parameter design and efficient application. In this paper, pressure wave propagation characteristics and mechanism in gas-liquid flow were investigated with a new proposed pressure wave velocity model that considers inter-phase mass transfer effect. This new model and its solution algorithm were verified with experimental data in literature. The influence of gas invasion stage, drilling fluid type, drilling fluid density and backpressure on pressure wave propagation characteristics were investigated. Results show that the time for pressure wave induced by wellhead backpressure in the wellbore cannot be ignored in the design of the backpressure value during MPD. This propagation time increases with occurrence of gas invasion. Moreover, the propagation time in water-based drilling fluid is longer than that in oil-based drilling fluid, which is because the interphase mass transfer between invaded gas and oil-based drilling fluid. The influence mechanism of high drilling fluid density and wellhead backpressure on pressure wave propagation characteristics is due to the suppression of gas invasion process. These findings could be used as guides in parameters design and optimization in MPD.

Effect of temporal nonlocality on wave propagation behaviors of viscoelastic FGM nanoshells

Effect of temporal nonlocality on wave propagation behaviors of viscoelastic FGM nanoshells

Investigation of Electromagnetic Wave Propagation in Triple Walled Carbon Nanotubes

This study examines the behavior of electromagnetic wave propagation in a unique and complex three-walled carbon nanotube structure. The structure is formed by nesting three distinct nanotubes, and the interactions between them are thoroughly analyzed, taking into account their varying electromagnetic, material, and nano properties. The structure is designed at a nanoscale to provide a comprehensive description of electromagnetic wave propagation, including the electromagnetic interaction between the second nanotube, located in the middle of the structure, and the other two nanotubes situated in both the inner and outer portions of the structure. This study presents novel findings that differ from existing literature on the subject, contributing to our understanding of this important area of research.

Wave propagation and multi-stopband behavior of metamaterial lattices with nonlinear locally resonant membranes

Wave propagation and stopband behavior in square lattices hosting nonlinear resonators made of suspended piezoelectric membranes with a central mass are investigated by treating asymptotically the wave propagation equations obtained via a projection method combined with the Floquet–Bloch theorem. The metamaterial membrane resonators made of a piezoelectric polymer are designed to exploit the piezoelectric effect which regulates the membrane stretching thus shifting the frequencies and, in turn, the bandgaps. Moreover, the resonators multi-modal behavior is tailored for its potential of generating multiple bandgaps for enhanced wave propagation control. The nonlinear dispersion functions of the metamaterial are obtained in closed form, and a numerical parametric analysis offers important hints on the design optimization. Numerical validations are also presented to verify the soundness of the analytical solutions and highlight the potential application of the semi-adaptively programmable metamaterial for wave propagation control.

Exact solutions of Shynaray-IIA equation (S-IIAE) using the improved modified Sardar sub-equation method

In this paper, we present an innovative approach to acquire the exact solutions of the Shynaray-IIA equations (S-IIAE), by using the improved modified Sardar sub-equation method (IMSSEM). The S-IIAE are nonlinear and coupled partial differential equations that arise in various fields of physics and engineering such as optical fibers and ferromagnetic materials. The IMSSEM is applied to S-IIAE; we successfully derived exact solutions that accurately described the wave propagation behavior of the system under consideration. The obtained solutions include rational, trigonometric, and trigonometric hyperbolic function solutions. The obtained solutions are concise and offer a deeper insight into the dynamics and characteristics of the S-IIAE. Moreover, some of the new solutions to S-IIAE are plotted in different dimensions through which bright, anti-kink and bright solitary wave structures are established. The results of the study also indicated that the proposed method is a valuable approach for achieving analytical solutions to a wide range of nonlinear partial differential equations.

Symmetry Breaking and Dynamic Transition in the Negative Mass Term Klein–Gordon Equations

Through the discussion of three physical processes, we show that the Klein–Gordon equations with a negative mass term describe special dynamics. In the case of two classical disciplines—mechanics and thermodynamics—the Lagrangian-based mathematical description is the same, even though the nature of the investigated processes seems completely different. The unique feature of this type of equation is that it contains wave propagation and dissipative behavior in one framework. The dissipative behavior appears through a repulsive potential. The transition between the two types of dynamics can be specified precisely, and its physical meaning is clear. The success of the two descriptions inspires extension to the case of electrodynamics. We reverse the suggestion here. We create a Klein–Gordon equation with a negative mass term, but first, we modify Maxwell’s equations. The repulsive interaction that appears here results in a charge spike. However, the Coulomb interaction limits this. The charge separation is also associated with the high-speed movement of the charged particle localized in a small space domain. As a result, we arrive at a picture of a fast vibrating phenomenon with an electromagnetism-related Klein–Gordon equation with a negative mass term. The calculated maximal frequency value ω=1.74×1021 1/s.

Transverse-inertia-induced wave dispersion in plate–shell chains with a variable Poisson ratio

One-dimensional shell chain structures can cause stress wave dispersion, and the dispersion ability is mainly affected by the apparent elastic Poisson ratio of the unit cell composing the chain. In this study, a novel plate–shell chain structure with a variable Poisson ratio is proposed by combining bent plates and arc shells (BPAS). The dispersive wave propagation features in the BPAS chains under striker impact are studied theoretically, numerically, and experimentally. An equivalent continuum model of the unit cell under compression in a linear-elastic deformation regime is established, which contains two material parameters, i.e., the apparent elastic modulus and the apparent elastic Poisson ratio. It is found that the unit cell can reach a relatively large Poisson ratio by adjusting its structural parameters. A continuum-based wave propagation model considering transverse inertia is developed, and an explicit analytical solution is obtained to represent the dispersion wave propagation behavior within a linear-elastic deformation regime. The model can reasonably predict the force and velocity evolution features of the chains and is verified by the numerical/experimental tests. The results show that the BPAS chain with a large Poisson ratio exhibits superior wave dispersion performances. The underlying mechanism is that more impact energy is dispersed by the transverse movement of the cells in the BPAS chain. Increasing the aspect ratio of the unit cell can improve the wave dispersion ability of the BPAS chains, achieving a high attenuation of the stress wave and is helpful for impact mitigation.

VARIATIONS IN MAGNETIC PROPERTIES PROPAGATION IN STEEL SHELL STRUCTURE CAUSED BY WELDING (PART 2)

The first stage of the research involves analyzing primary and secondary acoustic wave propagation behavior. The results of the first stage suggest that the properties of shell structures used at every stage of the experiment are distributed unevenly along the generator lines and across the width of the test pipes. In order to conduct a comparative study of properties, the authors of the research introduce the heterogeneity parameter. During the experiment, the parameter is changing locally within two orders of magnitude, even in case of test pipes in their initial state. Equal sensitivity to heterogeneities across steel products is found in its magnetic properties. As numerous studies prove, analyzing variations in magnetic properties makes it possible to detect flaws and areas of their concentration. This method can also be used to estimate the remaining service life. This is a crucial aspect to consider when assessing properties and using the findings to develop digital twins of shell structures. The authors focus on identifying acoustic and magnetic signals coming from flawed shell structures and weld joint areas in particular. For this purpose, magnetic memory method and X-ray analysis are used. It is found that both normal and tangential magnetic field components are sensitive to structural heterogeneities across a steel product. The combination of magnetic memory method and X-ray analysis make it possible to determine how typical weld joint flaws occurring during welding affect the magnetic properties. Sufficient measurements are required for statistical analysis of the findings. It is also possible to introduce further criteria in order to import metal properties correctly into the modelling program using numerical methods.

The Future of Flying Base Stations: Empirical and Numerical Investigations of mmWave-Enabled UAVs

Nowadays, wireless communications are ubiquitously available. However, as pervasive as this technology is, there are distinct situations, such as during substantial public events, catastrophic disasters, or unexpected malfunctions of base stations (BSs), where the reliability of these communications might be jeopardized. Such scenarios highlight the vulnerabilities inherent in our current infrastructure. As a result, there is growing interest in establishing temporary networks that offer high-capacity communications and can adaptively shift service locations. To address this gap, this paper investigates the promising avenue of merging two powerful technologies: Unmanned Aerial Vehicles (UAVs) and millimeter-wave (mmWave) transmissions. UAVs, with their ability to be operated remotely and to take flight without being constrained by terrestrial limitations, present a compelling case for being the cellular BSs of the future. When integrated with the high-speed data transfer capabilities of mmWave technology, the potential is boundless. We embark on a hands-on approach to provide a tangible foundation for our hypothesis. We carry out comprehensive experiments using an actual UAV equipped with an mmWave device. Our main objective is to meticulously study its radio wave propagation attributes when the UAVs are in flight mode. The insights gleaned from this hands-on experimentation are profound. We contrast our experimental findings with a rigorous numerical analysis to refine our understanding. This comparative study aimed to shed light on the intricacies of wave propagation behaviors within the vast expanse of the atmosphere.

Evaluating the effects of velocity models and array configuration on induced seismic event locations in the Permian Basin

In the final months of 2022, two substantial earthquakes with magnitudes exceeding ML 5.0 hit West Texas, USA, causing widespread public concerns about the effect of industrial activities on human and environmental safety. The monitoring of earthquakes in this region is largely based on the data of the public regional seismic array, which consists of stations spaced typically tens of kilometers apart. Accurate hypocenter determination of these induced events is crucial as it provides insight into the triggering mechanism, enabling operators and regulators to develop effective mitigation strategies. However, there are debates regarding the accuracy of the publicly reported induced event data due to discrepancies between public reports of event hypocenters and those determined using local dense arrays operated by private companies. The primary objective of this study is to identify the underlying causes of the discrepancies between results obtained from the public regional array in West Texas and local dense arrays. Through modeling and analysis of field data collected by a local dense array in the Permian Basin, we determine that three critical factors influence the reliability of induced event results. First, the accuracy of the velocity model used for the event location is the most crucial factor. Second, the distance between a station and an event plays a crucial role in determining the sensitivity of the data to the hypocenter depth. Finally, consistency between the observed and modeled wave propagation behavior is crucial for ensuring the validity of the objective function in the inversion. Our findings indicate that it is challenging to obtain reliable hypocenters using a regional sparse array with station spacing on the order of tens of kilometers. The best practice for obtaining an accurate event hypocenter and magnitude is to monitor induced seismicity using a local dense array and process the data with a velocity model that fully characterizes the local basin’s geology.